Silicone rubber compositions of the condensation curing type comprising an organopolysiloxane terminated with Si--OH groups as a base polymer and a silicon compound having a hydrolyzable group such as vinyltriacetoxysilane and vinyltriisopropenoxysilane as a crosslinking agent are used in a variety of applications. Such curable silicone rubber compositions of the one package type cure through the mechanism that condensation reaction takes place between Si--X groups (wherein X is typically acetoxy or isopropenoxy) in the crosslinking agent and Si--OH groups at the terminus of the base polymer to form siloxane bonds and then, excessive Si--X groups undergo hydrolytic condensation reaction under the action of moisture in the ambient atmosphere. In two package type compositions wherein the amount of the crosslinking agent used is equivalent to the amount of Si--OH groups at the terminus of the base polymer, curing can be completed solely by the condensation reaction between Si--OH groups and Si--X groups. In this case, moisture in the ambient atmosphere is not particularly required.
Also known from JP-A 234923/1994 is a fluorine-modified silicone rubber composition of the condensation curing type comprising an oily base polymer in the form of a fluorinated polyether having Si--OCH.sub.3 groups incorporated at its terminus. More particularly, this composition contains a compound of the following formula as the main component and cures through hydrolytic condensation of Si--OCH.sub.3 groups with moisture in the ambient atmosphere. ##STR1##
The resulting fluorine-modified silicone rubber is superior with respect to solvent resistance, chemical resistance, and stain resistance, as compared with prior art silicon rubber based on dimethylpolysiloxane. This silicone rubber, however, has the drawbacks that its moisture permeability is low because it is a polymer having a high fluorine content and that curing to the depth takes a long time because moisture in the ambient atmosphere is requisite for curing.